The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Multi-disk clutches are, for example, components frequently used in automotive engineering for the transmission of a torque or for the braking of a rotary movement. Multi-disk clutches of this type include internal disks rotationally fixedly connected to a clutch hub and external disks rotationally connected to a clutch basket. The internal and external disks are arranged alternately so that the disks are pressed together by axial actuation of the clutch. During the pressing together, the friction between the internal disks and the external disks increases, whereby the torque transmitted between the clutch hub and the clutch basket increases.
Multi-disk clutches of this type are generally known and are used in transmissions of different types, for example.
Drag torques in particular occur in oil-lubricated (wet running) multi-disk clutches in an open (disengaged) state of the clutch. In this connection, a torque is also transmitted between the clutch hub and the clutch basket in the disengaged state due to the viscosity of the oil, with the drag torque decreasing as the distance of the disks increases. To keep the drag torques small, multi-disk clutches have to be “opened” on disengaging. In this connection, adjacent disks are removed from one another directly or indirectly by a resetting device, for example in that a piston previously pressing the disks together is moved away from the disks until it adopts a disengaged position (abutment position) and thus liberates the disks for a mutual release. Provision is thus made by the resetting device that the disks again adopt a mutually spaced part position so that no-load torques or drag torques are minimized.
The setting dynamics of the clutch are defined, on the one hand, by the time duration to the passing through of the release distance and, on the other hand, by the time duration to the passing through of the clutch distance for the desired clutch torque. No real torque is yet transmitted—apart from a drag torque—during the passing through of the release distance. Such a dead time (i.e., the time from the demand for the torque until a torque is actually transmitted) degrades the response dynamics of the clutch and should, therefore, be minimized where possible.
With conventional clutches, much higher setting times or dead times are observed in a cold state (low temperature range), for example, shortly after putting the vehicle into operation, than in a warm state (operating temperature range). As the warming up of the clutch progresses, the setting dynamics of the multi-disk clutch improves again. The unsatisfactory setting dynamics in the temperature range is, for example, due to the fact that an electrically operated planetary rotor pump provided for the actuation of the clutch has poorer performance characteristics at low temperatures.
With some clutches, it is also seen that temperature fluctuations within the operating temperature range of the clutch have an effect on the setting times in an unwanted manner. This effect is considered due to a different thermal expansion of the different areas of the clutch which accompanies a change in the release distance.